Process for decolorizing mineral oil



June 8, 1943- w. B. cHENAuL'r ETAL 2,321,460

PROCESS FOR DECOLORIZING' MINERL OIL Filed Nov. 6, 1941 Patented June 8,17943 rnoonss Fon DECoLoRIzING MINERAL oIL William B. Chenault,Wellsville, N. Y., and Albert E. Miller, Westfield, N. J., assignors toSinclair Reining Company, New York, N. Y., a corporation of MaineApplication November 6, 1941, Serial No. 418,002 In Canada November 27,1940 6 Claims.

This invention relates to the refining of mineral cils, and moreparticularly, to the decolorizing of mineral oils. The inventionprovides an eiiicient and relatively inexpensive process for thecontinuous decolorization of mineral oils and the continuous recovery,reactivation and cyclic reuse of the materials used in, and inconnection with, the decolorization of such oils.

Numerous processes have been proposed heretofore and are now incommercial use in which mineral oils are subjected. to the action ofdecolorizing earths, that is, earths which have the property of removingobjectionable coloring matter from such cils. In general these processesemploy elevated temperatures in order to obtain eflicient contactbetween oil and decolorizing earth, and many of these processes electsuch contact in the presence of oxidizing atmospheres, such as air. Suchprocesses employing elevated tempera-tures, `generally in theneighborhood of about 500-650 F., whether conducted in an oxidizingatmosphere either intentionally or due to the presence of adventitiousair or air liberated from the grains of earth by the elevatedtemperatures, promote oxidation of the treated oil and of the coloringmatter removed from the oil by the decolorizing earth. Oxidation of thetreated oil is an obvious objection to these processes. Moreover,modication of the coloring matter removed from the oil and adsorbed bythe decolorizing earth which occurs at the elevated temperaturesemployed in such processes, and which is promoted by oxidation, preventsor renders impracticable reactivation of the spent earth with solvents.In the few instances where reactivation of the spent decolorizingearthfrom such processes may be accomplished with solvents, .large andcomplex mixtures of expensive solvents are required and even then thereactivated earth is not restored to its original high decolcrizingefliciency. Reactivation of spent decolorizing earth is necessary ifsuch decolorizing processes are to be commercially feasible.Regeneration of spent earth by burning such earth to restore itsdecolorizing efiiciency is accompanied by destruction of the grains ofearth with the production of an excessive quantity of earth too iine forefficient oil-earth separation. Moreover, when such earths regeneratedby burning are cooled, air is adsorbed by the grains of earth and thisair is subsequently liberated in situ in the oil by the elevatedtemperature employed in the decolorizing operations.

We have devised a novel process whereby mineral oils may be decolorizedwith decolorizing earths at moderately elevated temperatures withefficient and effective solvent reactivation of the decolorizing earthand with eiiicient and effective re-use of the decolorizing earth andthe materials used in its reactivation. Our process is adapted to becarried out continuously and in a closed system wherein a non-oxidizingatmosphere is maintained so that external disturbing inuences areeliminated. Y

In its broadest aspect our processinvolves admixing the oil to bedecolorized with reactivated decolorizing earth wet with naphtha fromthe iinal washing 'stage of the reactivating treatment hereinafterdescribed, with or without additional naphtha, and heating the mixturein a contact heater to an elevated temperature less than the criticaltemperature, approximating 450 F. with most oils, at which coloringmatter adsorbed from the oil by the earth becomes modied to anobjectionable extent precluding reactivation of the earth to a highdecolorizing eiciency by eXtraction with the usual color-solvents. Thismixture is maintained at an elevated temperature for a period of timeadequate to effect the desired degree of decolorization andthe spentearth is thereafter filtered, in a primary deoiling lter, from thedecolorized oil with or without intervening stripping `o1 the naphthapresent in the mixture subjected to the heating operation firstmentioned.

'Ihe primary de-oiling ltration is carried out at an elevatedtemperature which varies with the viscosity of the oil to be decolorizedand with the proportion of naphtha present in the liquid component ofthe mixture supplied to the filtering operation. The temperature andnaphtha content, if any, of` this liquid component are correlated tomaintain the viscosity of the liquid component at a value permittingfiltration at a high lter rate while avoiding substantial vaporization.Correlation of the temperature maintained in the primary de-oiling lterand of the naphtha content of the mixture supplied thereto so that theliquid component of the mixture will have a kinematic viscosity of 4-6centistokes at the temperature prevailing in the ltering operation willpermit filtration at the desired high lter rates. g

The spent earth separated from the decolorized oil, or from thedecolorized oil-naphtha blend, by this initial filtering operation isthen reactivated by subjecting it in succession to an initial washingwith naphtha, or equivalent oil-solvent, to remove oil retained by theearth, thereafter to an extraction treatment wherein the substantiallyoil-free spent earth in the form of a slurry is extracted with asuitable color-solvent for adsorbed coloring matter, such as acetone ormethyl ethyl ketone, and thereafter to a final washing treatment inwhich the reactivated earth is Washed with an additional quantity ofnaphtha to displace at least the major portion of the color-solventretained by' the earth. The thus reactivated earth wet with naphtha andin some instances containing a minor but significant proportion ofresidual color-solvent not removed in the nal naphtha washing treatment,is then slurried with such additional naphtha as may be necessary toform a pumpable mixture and returned to the contact heater firstmentioned where it is used in decolorizing additional oil. If desired,the oil-naphtha mixture resulting from the naphtha washing treatmentcomprising the initial stage of the reactivation, may be returned to thecontact heater for recovery of its oil component and further use of itsnaphtha component.

We have found that when the maximum temperature attained in thedecolorizing operation proper, i. e., in the contact heater, is limitedto a value less than about 200 F., adequate decolorization may beobtained if the contact treatment is effected when the oil is dilutedwith a relatively large amount of naphtha Varying from 25% to about 150%naphtha by volume on the oil depending on the viscosity of the oil beingtreated, and that at this relatively low temperature modification of theadsorbed coloring matter occurs, if at all, to an extent so negligiblethat the spent earth may be repeatedly reactivated by the abovedescribed procedure to a decolorizing efhciency not significantlydifferent from vthat of the original decolorizing earth. In thisrelatively low temperature and high naphtha dilution form of operation,the color-solvent may quite readily be removed almost completely fromthe reactivated earth in the final naphtha wash- 'ing stage of thereactivating operation. Accordingly', in this type of operation thetrace of residual color-solvent remaining in the earth returned to thecontact treatment is insignificant in that it does not appear to involvea significant loss of color-solvent and has no noticeable adverse effecton the decolorizing operation, a circumstance perhaps due in part to thelow temperature, to the relatively high ratio of decolorizing earth tooil, and to the relatively large volumes of naphtha employed as aconsequence of the relatively high earth to oil ratio. That modificationof our invention involving the use of very low temperatures and extremedilution is described in detail in our application, Serial No. 295,706,filed September 20, 1939.

One objection to this very low temperature embodiment of our inventionlies in the fact that the activity of the decolorizing eartlis isgreatly reduced at temperatures lower than 200 F. and this circumstancenot only increases the amount of decolorizing earth required to treat agiven amount of oil, but it also involves an increase in the size andcost of the equipment employed to carry out the decolorizing andreactivating operations together with a corresponding increase in thematerials used in the reactivating treatment.

The activity of most decolorizing earths increases rapidly with increasein temperature and we have found that if the earth-'oil mixture isheated in the contact heater to a temperature of 250-400 F. the desireddegree of decolorization can be effected in the absence of excessivenaphtha dilution in a time no longer than that required to heat the oilto this temperature even though the amount of earth incorporated in theoil is less than of that required to obtain the desired degree ofdecolorization with similar oils when the vmaximum temperature ismaintained at a value less than 200 F. We have also found thatmodification of the coloring matter adsorbed by the earth, whichaccompanies an increase in the temperature up to a critical valueapproximating 450 F. with most oils, is not of a character thatprecludes reactivation of the earth to a decolorizing efficiency atleast closely approaching that of the original earth by the procedureherein described. However, when using these higher temperatures and thelesser proportion of decolorizing earth thereby made permissible, thereis some modification of the adsorbed coloring matter and a somewhat morerigorous extraction with the color-solvent is required. Moreover, itappears to be more dicult to remove color-solvent retained by the earthWithout excessive naphtha washing. In any event, we have found that insuch higher temperature operations the residual color-solvent may reacha value as high as 3% by weight on the reactivated earth unlessexcessive naphtha washing is employed.

With the lesser amount of naphtha required as a diluent and lesserproportion of decolorizing earth permissible when using highertemperatures, the minor but nevertheless significant amount of residualcolor-solvent retained by the earth in the absence of excessive naphthawashing in the final stage of the reactivating treatment may thus becomean undesirable factor of significant proportions in that it tends bothto involve a significant loss of the relatively costly color-solventand, by its presence during the decolorizing operation, to impair thedecolorizing efficiency of the earth by opposing its decolorizingaction. However, in that form of our process wherein relatively highertemperatures are utilized to obtain high decolorizing activity and topermit the use of smaller proportions of decolorizing earth, and whereinexcessive naphtha washing is not resorted to in the final stage of thereactivating treatment, both of the abovementioned undesirable effectsare avoided by stripping the residual color-solvent from the mixture asdischarged from the contact-heater prior to separation of the earth fromthe oil. Such stripping advantageously may be effected by the containedheat of the mixture, that is by flash distillation, and it may beeffected in one or more stages. By such procedure the oil remains incontact with the decolorizing earth at an elevated temperature afterseparation of residual color-solvent and during the period immediatelypreceding separation of the earth from the decolorized oil. Accordingly,the presence of a relatively small proportion of residual color-solventin the earth while heating the earth-oil mixture to the temperatureattained in the contact heater is not particularly objectionable.

If desired, the naphtha content in the mixture undergoing heating in thedecolorizing operation proper, as well as any residual color-solvent,both may be flash stripped prior to separation of the earth from theoil. By so doing the oil is obtained directly from the initial filteringoperation in finished form. This procedure is particularly desirablewhen treating unstable oils. When the earth is separated from the oilbefore complete stripping of the naphtha it is necessary thereafter todistil off residual naphtha to obtain the decolorized oil in finishedform and such distillation, effected in the absence of earth, causes asignificant color reversion with unstable oils necessitating a finalbrightening treatment wherein the oil is again treated with freshdecolorizing earth.

When it is desired to strip completely both residual color-solvent andnaphtha from the oil prior to separation of the earth therefrom, it isadvantageous to employ a two-stage stripping operation wherein residualcolor-solvent is stripped in the first stage together with suchproportion of the naphtha as it may be necessary to remove in order toinsure complete stripping of the-residual color-solvent. The remainderof the naphtha may then be stripped in the second stage with the aid ofreduced pressure and steam. Steam should not be used to assist thestripping operation when employing only one stage or in l the firststage of a two-stage stripping operation,

in order to provide for recovery of the residual color-solventuncontaminated by moisture.

A desirable embodiment of that form of the process of our inventionwherein residual colorsolvent and naphtha both are stripped from the oilby an eicient two-stage stripping system prior to separation of theearth from the decolorized oil so that the decolorized oil is directlyobtained in finished form is described in our application Serial No.313,878, filed January 15, 1940.

When treating either an oil that is relatively stable or an oilcontaining coloring matter of a character that is modied to anundesirable extent by moderately elevated temperature, it usuall;7 isundesirable to attempt to strip completely both residual color-solventand naphtha from the decolorized oil prior to the separation of theearth therefrom. In order to effect such complete stripping by thecontained heat of the mixture discharged from the contact heater itusually is necessary either to heat to a temperature upwards of 400 F.or to resort to an excessively reduced pressure in the strippingoperation. This relatively high temperature s higher than is required toeiiect adequate decolorization if the heat requirements of the strippingoperation are ignored. Yet a temperature exceeding 400 F. modifies thecharacter of the adsorbed coloring matter contained in certain oils toan extent precluding solvent reactivation of the decolorizing earth to adecolorizing eiciency even closely approaching that of the originalearth.

Moreover, even with an oil which does not contain coloring matter of acharacter susceptible to such extreme modification, an appreciablemodification of the adsorbed coloring matter nevertheless occurs at atemperature as high as 400 F. Accordingly, the use of a temperaturehigher than that required to secure adequate decolorization, solely forthe purpose of supplying the heat requirements of the strippingoperation, involves an unnecessary reduction in the average decolornizing eiciency of the reactivated earth with a corresponding increase inthe amount of earth required, a sacrifice which is not necessary whenthe oil being treated is sufiiciently stable to resist signiiicant colorreversion when completing the stripping operation after separation ofthe decolorizing earth from the oil.

Even in the unusual case where the oil is not suiciently stable toresist significant color reversion when stripping after separation ofthe earth, and when the coloring matter contained in the oil is of acharacter which undergoes a substantial undesirable modiiication at thelowest contact heater temperature which will permit com'- pletestripping of the naphtha prior to separation of the earth, that form ofour process which avoids the higher temperatures incident to completeflash stripping of the naphtha prior to separation of the earth from theoil but in which intervening stripping of residual color-solvent isnevertheless obtained, may be employed satisfactorily. In such a caseone may merely employ a slight excess of the decolorizing earth so as todecolorize the oil to an extent greater than that desired in theiinished oil and thus allow forvthe color reversion which occurs'in thefinal stripping operation.

In that form of our process in which the maximum temperature attained inthe contact heater is maintained at a value high enough to obtain rapiddecolorizing action Without resorting to excessive naphtha dilution, andhigh enough to effect complete stripping of the residualr colorsolventcontained in the mixture subjected to heating in the decolorizingoperation proper, but not high enough to permit complete stripping ofthe naphtha by the contained heat of the oil prior to separation of thespent earth from the oil, it may be necessary to cool the bottomsfraction from the stripping operation to avoid difn ficulties incidentto substantial vaporization, in the primary deoiling filter, of thenaphtha component of the mixture supplied thereto. When naphtha ispresent in the mixture supplied to the primary deoiling filter, thefilter temperature should be maintained at F.-180 F. preferably about175 F. At these temperatures the naphtha content of the bottomsVfraction discharged from the stripping operation may not be high enoughto produce a viscosity suitable to permit the desired filter rates. Insuch cases additional naphtha may be introduced to theV bottoms fractionprior to its introduction into the primary deoiling filter. Suchadditional naphtha may be supplied at a relatively low temperature andmay be used to provide all or a part of the cooling where bothcoolingfand further naphtha dilution are necessary. Naphtha for suchdilution may be obtained from an extraneous source or from'other partsof the combined oil-decolorizing and earth-reactivating system. However,the naphtha used for this purpose should not contain color-solvent.Therefore, the mixture of color-solvent and naphtha flash stripped fromthe hot mixture discharged from the contact heater is not suitable forthis v purpose.

The oil-solvents useful in our process include any of the varioussolvents generally used for this purpose. It is only necessary that theoilsolvent shall be capable of dissolving oil, sufiiciently volatile tobe completely separable from the oil by distillation at relatively lowtemperatures, partially separable by distillation from thecolor-solvent, and that it have in itself substantiallyno solventcapacity for coloring matter adsorbed from the oil in the earth. We havefound that naphtha having an initial boiling point of 250"` F. and anend point of 350 F., is particularly adapted for use in our process.

Moreover, naphthas known as 2,00/300 or 30G/400 F., the proportion of:.-naphtha'will in most instances be substantially less than thatrequired in the very low temperature decolorizing operations previouslymentioned. Thus in the treatment of Pennsylvania neutrals using thatform of operation in which the reactivated earth is slurried with onlyenough naphtha to render it pumpable before admixing it with additionaloil preparatory to reintroducing it into the contact heater, thepercentage of naphtha to oil may be as low as 5% by volume on theoil-naphtha blend. On the other hand, when decolorizing viscousraflinates or cylinder stocks and employing that form of operation inwhich naphtha washings from the deoiling operation are introduced intothe contact heater for recovery of the oil removed from the spent earth,the proportion of naphtha in the oil-naphtha blend supplied to thecontact heater may vary from about 40% to 60%, or even higher,

A wide variety of finely-divided decolorizing earths may be used incarrying out the process of our invention. For example, finely-dividedfullers earth, activated bauxites, such as Porocel and acid-treatedbentonites, such as Filtrol, or Tonsil, may be used. We have found,however, that the snthetic adsorbent decolorizing earth known asMagnesol may be used with particular advantage. Magnesol is a synthetichydrated magnesium silicate normally obtained by rst preparing ahydrated calcium silicate and then reacting the calcium silicate withmagnesium chloride. If Magnesol is used, from 2% to about 16% of thedecolorizing earth on a dry basis by weight of oil treated may be usedwith advantage. We have found 8% to 12% of Magnesol to be particularlyadvantageous in decolorizing viscous raiiinates when employing a contactheater temperature approximating 350-400 F. These percentages will besomewhat increased when using reactivated clay, the increase dependingupon the decolorizing efciency of the reactivated clay. At temperaturesapproximating 250-350 F. this type of clay has a decolorizing activityexceeding by more than 50% that exerted at temperatures of l50-l90 F.,and the activity is further increased with still higher temperatures.When employing a clay such as Magnesol in the treatment of aPennsylvania neutral, adequate decolorization can be obtained in a timeno longer than that usually required to heat the oil to a temperatureapproximating 250 F. The corresponding temperature would approximate 350F. in the case of a viscous raffinate or cylinder stock.

We have investigated numerous color-solvents for removing from thedecolorizing earth coloring matter adsorbed from the oil, and have foundthat the lower alcohols and ketones may in our process be used for thispurpose with advantage. Thus, methyl, ethyl and isopropyl alcohols andsuch ketones as acetone, methyl ethyl ketone, methyl propyl ketone andmethyl isopropyl ketone may be used advantageously. These solventseither alone or in combination, and preferably in further admixture withnaphtha or equivalent oil-solvent, have been found to be particularlyefficient in the process of our invention. A mixture of one part ofmethyl ethyl ketone and two parts naphtha by volume has been used withparticular effectiveness. The abovementioned color-Solvents effectremoval of coloring matter from spent decolorizing earth at temperaturesranging from atmospheric temperature to about 150 F., or somewhathigher. However, we have found especially eicient results to beobtainable with an extraction temperature of about F. i

Other advantages of the process of our invention will be apparent fromthefollowing more detailed description of one specific embodiment of ourprocess with reference to the accompanying schematic drawing whichrepresents diagrammatically one arrangement of apparatus adapted tocarry out the process of our invention. In this further description ofour process we will describe, for the purpose of illustration, anembodiment of our invention in which Magnesol is used as thedecolorizing earth, in which naphtha is used as the oil-solvent, inwhich a solvent blend comprising one-third methyl ethyl ketone andtwo-thirds naphtha is used as the color-solvent, in which only a singlestage stripping operation is interposed between the contact heater andthe primary deoiling filter, and in which the oil-earth solvent mixturein the contact heater is heated to a temperature permitting completestripping of the color-solvent but in which no attempt is made tocompletely strip the naphtha component by the contained heat of themixture discharged from the contact heater.

Referring to the drawing, oil to be decolorized, preferably preheated toa temperature of approximately F. or somewhat higher, is introducedthrough line I into contact heater feed tank 2 of the enclosed type. Theoil is mixed in this tank with reactivated decolorizing earth wet withnaphtha and containing a minor amount of color-solvent from sourceshereinafter more fully discussed. Continuous mixing and contact areprovided by conventional mechanical means, assisted, if desired, byrecirculation from the bottom to the top of the tank by means of acirculating pump. The earth-oil-naphtha mixture, in the form of aslurry, is delivered through line 3 into contact heater or heaters 4. Inthe contact heater, which may comprise a direct fired pipe still, orpipe stills, the temperature of the mixture is raised to an outlettemperature approximating 250-400 F. depending upon the nature of theoil being treated and the temperature required to effect substantiallycomplete vaporization of the color-solvent present, as above described.Under these conditions approximately the desired degree ofdecolorization is completed by the time the mixture reaches the outletof heater 4. When more than one heater is employed the heaters may bearranged either in series or in parallel. The hot mixture is thendelivered through line 5 into flash tower 6.

The color-solvent contained in the earth supplied to heater feed tank 2is taken ofi as an overheadvapor fraction from ash tower 6 together withsuch proportion of naphtha as may be necessary to insure completestripping of the colorsolvent. This vapor fraction is condensed incooler 1 and the resultant condensate may be conveyed to thecolor-solvent recovery unit l0.

The bottom fraction from tower 6 consists of the decolorized oil and theearth contained in the mixture discharged from the contact heater 4,together with such naphtha as is not removed in the overhead from tower6. This mixture is still at an elevated temperature and furtherdecolorization occurs in the bottom of flash tower 6 where'there is noopposing action by the colorsolvent present in the contact heater 4.

The bottoms fraction from flash tower 6 is conveyed alternativelythrough line 8, cooler 9 and line I2, or through line 8, by-pass Il andline l2, to primary deoiling filter I3. While passing from flash tower 6to primary deoiling filter I3 the temperature of the bottoms fraction isreduced to a Value approximating l50180 F.,

preferably about 175 F., if its temperature exceeds this value asdischarged from the flash tower. Prior to introduction into the primarydeoiling filter I3 which is preferably a continuous rotary vacuumfilter, additional naphtha may be added to the mixture through line I9in a quantity sufhcient to bring the viscosity of the liquid componentof the mixture entering the filter to a Value not higher than 40 secondsSaybolt Universal at the temperature maintained in the filter I3 if thenaphtha content of the bottoms fraction discharged from fiash tower 6 isless than this value. It will be appreciated that these low viscositiescannot be accurately determined directly and can be ascertained only byactually determining the kinematic viscosities in centistokes and thenconverting to Saybolt Universal viscosities. At a temperatureapproximating 175 F. a suitable viscosity is obtained with a blend ofwhich the liquid component comprises approximately 70% oil and 30%naphtha when the oil is a neutral, or 50% oil and 50% naphtha when theoil is a viscous raffinate` By maintaining a temperature approximatingl50180 F. in the filter I3, substantial vaporization of the naphthapresent may be avoided. Moreover, significant color reversion of thedecolorized oil through oxidation by adventitious air is avoided at thistemperature.

When the naphtha 'content ofthe bottoms as discharged from fiash tower 6is high enough to produce the desired viscosity at the temperatureprevailing inv filter I3, no additional naphtha need be supplied at I9,andthe requisite cooling, if cooling is required, may be effected incooler 9. On the other hand, when the amount lof naphtha required to besupplied through I9 is substantial, and when cooling also is required,all of the requisite cooling of the vbottoms from flashtower may beeffected in this manner. In either the latter case or when no cooling isrequired, the cooler may be by-passed as'indicated at II.

In filter I3 the spent decolorizing earth is separated from the naphthasolution of decolorized oil which then passes through line I4 to astripping still'conventionally illustrated at I5. The filter cake formedin filter I3 may be washed in a section of the filter with naphthasupplied through line 20. The initial washings, containing a relativelylarge proportion of decolorized oil, may be discharged through line I4to stripping still I5. Subsequent washings may be returned via lines 28and 29 to the contact heater feed' tank 2.

In still I5 the principalA filtrate from Afilter I3 should be strippedunder a sufficiently reduced pressure or with a sufficient amount ofsteam to avoid color reversion when the oil being decolorized isrelatively stable, such as an oil which has been stabilized by solventextraction. The naphtha stripped in I5 passes through condenser Il tonaphtha storage tank I8 for re-use in the system. The bottoms fractiondischarged from I5 through line I6 normally represents the finisheddecolorized oil; If cloudy, it may be passed through a conventionalblotter-paper filter press before passing to finished oil beingprocessed is one of those oils which would be subject toV some colorreversion during the step of distilling off the naphtha in I5, the oilVmay initially be decolorized to a point slightly beyond the colordesired in the finished product in order to allow for the slight colorreversion storage. If the oil encountered in the stripping operation.This may be done, for example, by slightly increasing the ratio ofdecolorizing earth to oil vin the mixture supplied to contact heater 4.

The spent earth separated in the primary deoiling filter i3 passes vlaconveyor 2| to deoiling slurry tank 22 where it is reduced to the formof a pumpable slurry with additional naphtha supplied through line 25.This slurry may contain about 20-25.% by weight of spent earth on a drybasis and about %"/5% by weight of naphtha. This slurry is suppliedthrough line 23 to secondary deoiling filter 24 which, like filter I3,also is preferably a continuous rotary vacuum filter. The filter cakewhich forms in secondary deoiling filter 24 may be subjected toadditional washing with naphtha supplied at 30 to remove more completelyany oil retained by the spent decolorizing earth. The primary filtratefrom filter 24 may be returned to the contact heater feed tank 2 vialines 26, (i9, 48 and 29 for recovery of its oil component and furtheruse of its naphtha content. The secondary filtrate or final washingsfrom filter 24 advantageously are conveyed through line 25 to deoilingslurry tank 22 to, provide the naphtha employed therein.

The washed filter cake obtained from the secondary `deoiling filter 24,comprising approximately equal parts by weight of naptha and spentearth, is removed continuously from the filter and carried by conveyor21 to spent-earth slurry mix tank SI. Here the earth again is mixedwitha sufficient quantity of naphtha to produce a pumpable slurry containingabout 25- 30% by weight of earth, This naphtha may be supplied throughline 32. The slurry thus obtained is pumped through line 33 intospent-earth extractor 34 which is )provided` with conventional mixingmeans whereby the spent earth is extracted by highlyrefcient admixturewithv the color-solvent, which, under the conditions just described, maycomprise a blend of methyl ethyl ketone and naphtha. The color-solventblend supplied through line 35 is preferably preheated to a temperatureof about--150o F. before introduction into extractor 34. `A temperatureof about 100 -l 50 F., and preferably about 130- l50 F., is maintainedin extractor 34 in order to enhance the solubility of the coloringmatter in the color-solvent, The resulting slurry comprising about l520%v by weight of solvent-extracted earth together with naphtha,color-solvent and the coloring matter dissolved therein, then Apassesthrough line 3S into reactivated earth filter unit 3i. This filter unitmay comprise one or more continuous rotary vacuum type filtersmaintained at an operating temperature of about 100 F. to about F.,higher temperatures promoting higher filtering rates with the actualtemperature depending to an important extent upon the boiling point ofthe color-solvent and the vacuum maintained on the filter unit. Themajor portion of the color-solvent is washed from theV filter cake whichforms in 37 by means of naphtha supplied through line 33. Y

The first filtrate from reactivating filter 31, containing a relativelyhigh concentration of color-solvent, passes via line39 to color-solventrecovery unit I 0 in which coloring matter, removed from the treated oilby the earth and dissolved out of the earth by the color-solvent, isremoved and discarded. The recovered blend of color-solvent and anappropriate quantityA of naphtha to make up the desired color-solventblend is discharged from the solvent recoveryunit through line 35, whilenaphtha in excess of that desired in the color solvent blend isdischarged from the color-solvent recovery unit through line 40 and maybe either returned to naphtha storage tank I8 or directly supplied toother points in the system where naphtha is required. The iinal washingsfrom lter 31 may be conveyed through line 32 to slurry tank 3l with orWithout additional naphtha for use in producing the slurry supplied toextractor 34.

Thewashed filter cake obtained from reactivated earth lter 31, normallycomprising reactivated earth of high eiciency containing about an equalamount of naphtha and 0.5% to 1.5% of color-solvent, passes Via conveyor42 to the reactivated earth slurry mix tank 43 wherein it is worked upinto a thick pumpable slurry with additional naphtha supplied from tankI8 via lines 41 and 44. Naphtha for this purpose may be supplied toslurry mix tank 43 as a blend consisting predominantly of naphthaderived from filter I3 via lines 28 and 45 or from lter 24 via lines 2S,46 and 44. The slurry thus obtained, containing about 28-30% by weightof earth on a dry basis and the balance essentially of naphtha, is thendelivered through lines 29 into contact heater feed tank 2 as the sourceof the decolorizing earth, and at least in part the source of thenaphtha to be admixed with the oil to be decolorized to form theearth-oil-naphtha mixture that supplies the contact heater. Whenadditional naphtha is desired in the mixture supplied to contact heater4 it may be directly introduced into line 29 from naphtha storage tankI8 via lines 41 and 48, or supplied to line 29 as a blend consistingpredominantly of naphtha from lter I3 via line 28 or from lter 24 vialines 26, 49 and 48.

Where it is not desired to de-oil the spent earth to a very low oilcontent prior to extraction of the color solvent, adequate deoiling maybe obtained in the primary filter unit I3. Under these circumstances thewashed clay cake may be conveyed directly from lter I3 to slurry mixtank 3l via conveyors 2|, 50 and 21. In this simplified arrangement,which may be desirable in small installations, the slurry tank 22 andsecondary deoiling filter 24 need not be provided.

It will be appreciated by those skilled in the art that the foregoingdescription is concerned only with the more essential details of ourprocess and that in practice a system such as that schematicallyillustrated in the drawing normally will be provided with the usualfiltrate receivers, pumps, and the like, which have not been specicallyillustrated nor described. Similarly, it will be obvious that suchelements as the conveyors 2|, 23, 21, 42 and 50, slurry tanks 22, 3I and43, and lters I3, 24 and 31, should be of the enclosed type to avoidloss of solvents through evaporation. will also appreciate that Whereadventitious air and volatile solvents ordinarily might be presentsimultaneously in zones of elevated temperature, as in the vacuumfilters I3, 24 and 31, an atmosphere of inert or non-oxidizing gas, suchas flue gas, should be provided. This inert gas may be utilized to blowthe filter cake lfrom the filter units.

We claim:

1. In a process for decolorizing mineral oils the improvement whichcomprises heating the oil to be decolorized, in admixture with areactivated decolorizing earth wet with naphtha and containingarelatively small amount of a color-` solvent more volatile .than thenaphtha andV capable of extracting from the earth coloring matteradsorbed from the oil by the earth, to a temperature upwards of about200 F. and less than about 450 F. but high enough at least to vaporizesaid color-solvent substantially completely and to effect approximatelythe desired degree of oil decolorization in the time required to attainsaid temperature, discharging the heated mixture into a stripping zoneand therein in the absence of moisture stripping at least thecolor-solvent substantially completely and a part of the naphtha fromthe mixture by the contained heat of the mixture, filtering the spentearth from a mixture comprising the bottoms fraction discharged fromsaid stripping zone prior to further contact with the color-solvent,reactivating the spent earth by subjecting it `firstly to washing withnaphtha to remove oil Those skilled in the art retained by the spentearth, secondly to an extraction treatment in which the spent de-oiledearth in the form of a slurry is extracted withy a color-solvent capableof extracting from the earth coloring matter adsorbed from the oil bythe earth, and thirdly to a further washing with naphtha wherein themajor portion of the retained color-solvent is displaced from thereactivated earth, and returning the 'reactivated earth wet with naphthaand containing a minor proportion of the color-solvent to the heatingoperation rst mentioned.

2. The method of decolorizing oil which comprises subjecting the oil inthe presence of naphtha to the action of a decolorizing earth at anelevated temperature and for a period of time adequate to effectsubstantial decolorization of the oil, separating the earth from thedecolorized oil, reactivating the separated earth by subjecting it inthe form of a slurry to the action of a color solvent capable ofextracting from the earth the coloring matter removed from the` oil bysaid earth, washing the reactivated earth withn naphtha to remove colorsolvent and coloring matter contained therein, and returning the washedreactivated earth wet with naphtha to the oil-decolorizing operation.

3. The method of decolorizing oil which comprises subjecting the oil inthe presence of naphtha to the action of a decolorizing earth at atemperature in the range substantially above atmospheric and up to about450 F. such as to eiect the desired degree of decolorization during thetime the mixture remains at said elevated temperature, separating theearth from the decolorized oil, reactivating the separated earth bysubjecting it in the form of a slurry to the action of a color solventcapable of extracting from the earth the coloring matter removed fromlthe oil by said earth, Washing the reactivated earth with naphtha toremove color solvent and' coloring matter contained therein, andreturning the washed earth wet with naphtha to the.

oil-decolorizing operation.

4. A continuous process for decolorizing oil by contact with adecolorizing earth and reactivating the earth for re-use, whichcomprises heating a mixture of the oil and decolorizing earth in thepresence of naphtha to an elevated temperature at which coloring mattercontained in the oil is extracted by the earth, separating the earthfrom the decolorized oil, reactivating Athe separted earth by successiveWashings, rst with naphtha, then with a color solvent capable ofextracting from the earth the coloring matter absorbed from the oil andthen with naphthaL the earth being contacted with the color solvent inthe form of a slurry during the second mentioned Washing, and returningreactivated earth wet with naphtha from the last mentioned washingtreatment to the heating treatment rst mentioned.

5. The method of decolorizing oil which comprises heating a mixture ofthe oil and reactivated decolorizing earth in the presence of naphthaand residual color solvent to an elevated temperature for a period oftime adequate to effect substantial decolorization, passing the heatedmixture to an evaporating zone and there evaporating residual colorsolvent from the earth-oil mixture While said mixture remains at anactive decolorizing temperature, subsequently separating the earth fromthe decolorized oil, reactivating the separated earth by subjecting itin the form of a slurry to the action of a color solvent capable ofextracting from the earth the coloring matter removed from the oil bysaid earth, washing the reactivated earth with naphtha to remove asubstantial part of the color solvent retained by the earth, andreturning the reactivated earth wet with naphtha and containing residualcolor solvent from the last mentioned Washing treatment to the heatingtreatment lrst mentioned.

6. The method of decolorizing oil which cornprises heating a mixture ofthe oil and a decolorizing earth in the presence of naphtha to anelevated temperature substantially above atmospheric temperature atwhich coloring matter contained in the oil is extracted by the earth,stripping naphtha from the heated mixture of earth and oil, subsequentlyseparating the earth from the decolorized oil, reactivating theseparated earth by subjecting it in the form of a slurry to the actionof a color solvent capable of extracting from the earth the coloringmatter removed from the oil by said earth, Washing the reactivated earthwith naphtha to remove a substantial part of the color solvent retainedby the earth, and returning the washed reactivated earth Wet withnaphtha to the heating operation Iirst mentioned.

ALBERT E. MILLER. WILLIAM B. CHENAULT.

